Device and Method for Determining the Position of a Working Surface of a Working Disc

Abstract

A device for determining the position of a working surface of a working disc of a double-sided machine tool, a double sided grinder in particular, wherein the double-sided machine tool has two working discs, which form a working gap for double sided machining of work pieces between working surfaces facing each other, and of which at least one is rotatingly drivable, wherein the device comprises an optical measurement device having a radiation source, an optical detector device, and an analysis device, designed for being disposed outside of the working gap.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This is a national stage application of PCT / EP2011 / 000043 Filed on Jan. 7, 2011, the entire content of which are hereby incorporated by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH[0002]Not applicable.BACKGROUND OF THE INVENTION[0003]The present invention relates to a device for determining the position of a working surface of a working disc of a double-sided machine tool, a double sided grinder in particular, wherein the double-sided machine tool has two working discs, which form a working gap for double sided machining of work pieces between working surfaces facing each other, and of which at least one is rotatingly drivable, wherein the device comprises an optical measurement device having a radiation source, an optical detector device, and an analysis device, designed for being disposed outside of the working gap. The invention relates also to a method for determining the position of a working surface of a working disc o...

AI Technical Summary

Benefits of technology

[0009]Starting from the known state of the art, the present invention is based on the objective to provide a device and a method of the kind mentioned in the beginning, by which the position of the working surface of a working disc can be reliably determined even at narrow working gap and in the operation of the machine tool.

[0018]According to the present invention, a distance, a vertical distance in particular, of the working surface relative to a reference position is determined for determining the position of the working surface, for instance to a reference position of the optical measurement device. For instance, the distance of the working surface to a point on the deflecting surface of the beam guiding device or to a reference point of the detector device can be determined, the locations of these points being known. On the one hand, the present invention is based on the idea that the components of the optical measurement device which require greater constructional space are disposed outside the working gap, wherein by means of the beam guiding device, only the measuring beam is introduced into the working gap and guided out of it again. Thus, the part of the device disposed within the working gap occupies only a very small constructional space, so that the measurement is possible without problems even at very narrow working gaps. Moreover, the beam guiding device comprises a fluid supply, by means of which the region around the exit opening of the radiation and in particular that between the exit opening and the working surface can be flushed free, so that disturbing influences through machining media, like cooling lubricant e.g., do not occur. A gas or a liquid can be supplied for flushing via the fluid supply. Nitrogen, pressurized air, water, oil are mentioned by way of example. The measurement according to the present invention should take place comparably near to the edge of the working disc or of the working surface, respectively, because this edge is particularly critical with respect to wear. The components of the optical measurement device outside of the working gap, namely the radiation source, the detector device and the analysis device in particular, can be arranged in a protection casing outside of the working gap or the perimeter of the working disc, respectively, in order to be protected against accumulation of dirt or entrance of machining media.

[0020]It was demonstrated that the position of the working surface can be safely measured by the method of the present invention or the device of the present invention, respectively, with a measurement error of less than 5 μm on a working gap having a width of not more than 2 mm, even during a running machining process, a grinding process in particular.

[0025]Further measures can then be taken on this basis. For example, the machining process can be stopped when a given limit difference between the measured working surface profile and the desired profile is exceeded. The operator of the machine can also be given a message, for example that a dressing process is necessary for the working discs. It is also possible to select an optimum dressing process for the working discs from the respective measured surface profile of the working disc by means of the analysis device, the process generating minimum wear on the dressing tool and on the working disc. In machining tools with planetary kinematics in particular, the early detection of a change of the working disc profile can be compensated by suitable adaptation of the process parameters, so that the number of necessary dressing actions is reduced altogether. The adaptation of the process parameters can be selected automatically or manually on the basis of the analysis data of the analysis device.

[0029]However, it is also possible that the double sided machine tool works according to the principle of planetary kinematics, that is to say, at least one rotor disc is disposed in the working gap, said rotor disc receiving work pieces to be machined in recesses and being adapted to be rotated by means of a roll off device, whereby the at least one rotor disc, and together with it the work pieces received therein, move in the working gap along cycloidal paths. Here, the advantage is that in particular when the working disc is adjustable, the disc shape can be measured also, a disc topography in particular. This can be of decisive importance in the adaptation of machines with planetary kinematics.

Problems solved by technology

In this, it is a problem that variations in the basic parameters cannot be accounted for.

Even small variations of such basic parameters can have significant influence on the in-feed ratio, but remain often undetected by an operator in practice.

In the so-called feed-through grinding in particular, there is a comparably high wear when conventional grinding tools (for instance corundum discs) are used.

This wear has to be compensated, because otherwise the machined work pieces would become thicker and thicker.

However, it is a problem that the two working discs on such a double sided grinder do not necessarily wear in the same way.

Thus, uniform in-feed of the working discs results in a crawl drift of the working gap.

However, because each dressing process annihilates a comparably great amount of the volume of the grinding disc, this way of referencing is sumptuous and undesired.

The same problem can occur in machine tools with planetary kinematics, in which the work pieces are held in rotor discs and are moved in the working gap along cycloidal paths.

However, both measurement methods have the drawback that they yield steadily good measurement data only at standstill of the machining tool.

Mechanical measurement tracers as known from DE 24 27 709 A1 are subject to significant wear upon measurements on a running machine tool, a grinder in particular, when they come into contact with the working surface.

This problem could not be resolved even by optimized designs of the sensors with respect to shaping, coating or reduction of the tracking force.

The known optical systems are hampered by the fact that during the operation of the machining tool, there will be machining media, like for instance cooling lubricants, and rubbed-off particles in the measurement area between sensor and working disc, whereby the measurement is negatively affected or made impossible.

Thus, the machining process has to be interrupted for measurement, which is undesired in principle.

However, only a change of the surface speed of a working disc can be detected by this method, which change occurs in particular when a circumferential working disc running at constant speed experiences reduction of its diameter through wear.

However, wear of an abrasive layer on the front side of a grinding disc cannot be determined by this method, neither a position change of an abrasive layer.

A particular problem in the measurement at running operation of double sided machine tools is the usually very narrow working gap.

Known sensors cannot be used for measurement in the working gap for this reason.

Images